use std::cmp;
use std::io;
use std::io::prelude::*;
use std::mem;

#[cfg(feature = "tokio")]
use futures::Poll;
#[cfg(feature = "tokio")]
use tokio_io::{AsyncRead, AsyncWrite};

use super::{GzBuilder, GzHeader};
use super::{FCOMMENT, FEXTRA, FHCRC, FNAME};
use crc::CrcReader;
use deflate;
use Compression;

fn copy(into: &mut [u8], from: &[u8], pos: &mut usize) -> usize {
    let min = cmp::min(into.len(), from.len() - *pos);
    for (slot, val) in into.iter_mut().zip(from[*pos..*pos + min].iter()) {
        *slot = *val;
    }
    *pos += min;
    return min;
}

pub(crate) fn corrupt() -> io::Error {
    io::Error::new(
        io::ErrorKind::InvalidInput,
        "corrupt gzip stream does not have a matching checksum",
    )
}

fn bad_header() -> io::Error {
    io::Error::new(io::ErrorKind::InvalidInput, "invalid gzip header")
}

fn read_le_u16<R: Read>(r: &mut R) -> io::Result<u16> {
    let mut b = [0; 2];
    r.read_exact(&mut b)?;
    Ok((b[0] as u16) | ((b[1] as u16) << 8))
}

pub(crate) fn read_gz_header<R: Read>(r: &mut R) -> io::Result<GzHeader> {
    let mut crc_reader = CrcReader::new(r);
    let mut header = [0; 10];
    crc_reader.read_exact(&mut header)?;

    let id1 = header[0];
    let id2 = header[1];
    if id1 != 0x1f || id2 != 0x8b {
        return Err(bad_header());
    }
    let cm = header[2];
    if cm != 8 {
        return Err(bad_header());
    }

    let flg = header[3];
    let mtime = ((header[4] as u32) << 0)
        | ((header[5] as u32) << 8)
        | ((header[6] as u32) << 16)
        | ((header[7] as u32) << 24);
    let _xfl = header[8];
    let os = header[9];

    let extra = if flg & FEXTRA != 0 {
        let xlen = read_le_u16(&mut crc_reader)?;
        let mut extra = vec![0; xlen as usize];
        crc_reader.read_exact(&mut extra)?;
        Some(extra)
    } else {
        None
    };
    let filename = if flg & FNAME != 0 {
        // wow this is slow
        let mut b = Vec::new();
        for byte in crc_reader.by_ref().bytes() {
            let byte = byte?;
            if byte == 0 {
                break;
            }
            b.push(byte);
        }
        Some(b)
    } else {
        None
    };
    let comment = if flg & FCOMMENT != 0 {
        // wow this is slow
        let mut b = Vec::new();
        for byte in crc_reader.by_ref().bytes() {
            let byte = byte?;
            if byte == 0 {
                break;
            }
            b.push(byte);
        }
        Some(b)
    } else {
        None
    };

    if flg & FHCRC != 0 {
        let calced_crc = crc_reader.crc().sum() as u16;
        let stored_crc = read_le_u16(&mut crc_reader)?;
        if calced_crc != stored_crc {
            return Err(corrupt());
        }
    }

    Ok(GzHeader {
        extra: extra,
        filename: filename,
        comment: comment,
        operating_system: os,
        mtime: mtime,
    })
}

/// A gzip streaming encoder
///
/// This structure exposes a [`BufRead`] interface that will read uncompressed data
/// from the underlying reader and expose the compressed version as a [`BufRead`]
/// interface.
///
/// [`BufRead`]: https://doc.rust-lang.org/std/io/trait.BufRead.html
///
/// # Examples
///
/// ```
/// use std::io::prelude::*;
/// use std::io;
/// use flate2::Compression;
/// use flate2::bufread::GzEncoder;
/// use std::fs::File;
/// use std::io::BufReader;
///
/// // Opens sample file, compresses the contents and returns a Vector or error
/// // File wrapped in a BufReader implements BufRead
///
/// fn open_hello_world() -> io::Result<Vec<u8>> {
///     let f = File::open("examples/hello_world.txt")?;
///     let b = BufReader::new(f);
///     let mut gz = GzEncoder::new(b, Compression::fast());
///     let mut buffer = Vec::new();
///     gz.read_to_end(&mut buffer)?;
///     Ok(buffer)
/// }
/// ```
#[derive(Debug)]
pub struct GzEncoder<R> {
    inner: deflate::bufread::DeflateEncoder<CrcReader<R>>,
    header: Vec<u8>,
    pos: usize,
    eof: bool,
}

pub fn gz_encoder<R: BufRead>(header: Vec<u8>, r: R, lvl: Compression) -> GzEncoder<R> {
    let crc = CrcReader::new(r);
    GzEncoder {
        inner: deflate::bufread::DeflateEncoder::new(crc, lvl),
        header: header,
        pos: 0,
        eof: false,
    }
}

impl<R: BufRead> GzEncoder<R> {
    /// Creates a new encoder which will use the given compression level.
    ///
    /// The encoder is not configured specially for the emitted header. For
    /// header configuration, see the `GzBuilder` type.
    ///
    /// The data read from the stream `r` will be compressed and available
    /// through the returned reader.
    pub fn new(r: R, level: Compression) -> GzEncoder<R> {
        GzBuilder::new().buf_read(r, level)
    }

    fn read_footer(&mut self, into: &mut [u8]) -> io::Result<usize> {
        if self.pos == 8 {
            return Ok(0);
        }
        let crc = self.inner.get_ref().crc();
        let ref arr = [
            (crc.sum() >> 0) as u8,
            (crc.sum() >> 8) as u8,
            (crc.sum() >> 16) as u8,
            (crc.sum() >> 24) as u8,
            (crc.amount() >> 0) as u8,
            (crc.amount() >> 8) as u8,
            (crc.amount() >> 16) as u8,
            (crc.amount() >> 24) as u8,
        ];
        Ok(copy(into, arr, &mut self.pos))
    }
}

impl<R> GzEncoder<R> {
    /// Acquires a reference to the underlying reader.
    pub fn get_ref(&self) -> &R {
        self.inner.get_ref().get_ref()
    }

    /// Acquires a mutable reference to the underlying reader.
    ///
    /// Note that mutation of the reader may result in surprising results if
    /// this encoder is continued to be used.
    pub fn get_mut(&mut self) -> &mut R {
        self.inner.get_mut().get_mut()
    }

    /// Returns the underlying stream, consuming this encoder
    pub fn into_inner(self) -> R {
        self.inner.into_inner().into_inner()
    }
}

#[inline]
fn finish(buf: &[u8; 8]) -> (u32, u32) {
    let crc = ((buf[0] as u32) << 0)
        | ((buf[1] as u32) << 8)
        | ((buf[2] as u32) << 16)
        | ((buf[3] as u32) << 24);
    let amt = ((buf[4] as u32) << 0)
        | ((buf[5] as u32) << 8)
        | ((buf[6] as u32) << 16)
        | ((buf[7] as u32) << 24);
    (crc, amt)
}

impl<R: BufRead> Read for GzEncoder<R> {
    fn read(&mut self, mut into: &mut [u8]) -> io::Result<usize> {
        let mut amt = 0;
        if self.eof {
            return self.read_footer(into);
        } else if self.pos < self.header.len() {
            amt += copy(into, &self.header, &mut self.pos);
            if amt == into.len() {
                return Ok(amt);
            }
            let tmp = into;
            into = &mut tmp[amt..];
        }
        match self.inner.read(into)? {
            0 => {
                self.eof = true;
                self.pos = 0;
                self.read_footer(into)
            }
            n => Ok(amt + n),
        }
    }
}

impl<R: BufRead + Write> Write for GzEncoder<R> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.get_mut().write(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        self.get_mut().flush()
    }
}

/// A gzip streaming decoder
///
/// This structure exposes a [`ReadBuf`] interface that will consume compressed
/// data from the underlying reader and emit uncompressed data.
///
/// [`ReadBuf`]: https://doc.rust-lang.org/std/io/trait.BufRead.html
///
/// # Examples
///
/// ```
/// use std::io::prelude::*;
/// use std::io;
/// # use flate2::Compression;
/// # use flate2::write::GzEncoder;
/// use flate2::bufread::GzDecoder;
///
/// # fn main() {
/// #   let mut e = GzEncoder::new(Vec::new(), Compression::default());
/// #   e.write_all(b"Hello World").unwrap();
/// #   let bytes = e.finish().unwrap();
/// #   println!("{}", decode_reader(bytes).unwrap());
/// # }
/// #
/// // Uncompresses a Gz Encoded vector of bytes and returns a string or error
/// // Here &[u8] implements BufRead
///
/// fn decode_reader(bytes: Vec<u8>) -> io::Result<String> {
///    let mut gz = GzDecoder::new(&bytes[..]);
///    let mut s = String::new();
///    gz.read_to_string(&mut s)?;
///    Ok(s)
/// }
/// ```
#[derive(Debug)]
pub struct GzDecoder<R> {
    inner: GzState,
    header: Option<GzHeader>,
    reader: CrcReader<deflate::bufread::DeflateDecoder<R>>,
    multi: bool
}

#[derive(Debug)]
enum GzState {
    Header(Vec<u8>),
    Body,
    Finished(usize, [u8; 8]),
    Err(io::Error),
    End
}

/// A small adapter which reads data originally from `buf` and then reads all
/// further data from `reader`. This will also buffer all data read from
/// `reader` into `buf` for reuse on a further call.
struct Buffer<'a, T: 'a> {
    buf: &'a mut Vec<u8>,
    buf_cur: usize,
    buf_max: usize,
    reader: &'a mut T
}

impl<'a, T> Buffer<'a, T> {
    fn new(buf: &'a mut Vec<u8>, reader: &'a mut T) -> Buffer<'a, T> {
        Buffer {
            reader,
            buf_cur: 0,
            buf_max: buf.len(),
            buf,
        }
    }
}

impl<'a, T: Read> Read for Buffer<'a, T> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        if self.buf_cur == self.buf_max {
            let len = self.reader.read(buf)?;
            self.buf.extend_from_slice(&buf[..len]);
            Ok(len)
        } else {
            let len = (&self.buf[self.buf_cur..self.buf_max]).read(buf)?;
            self.buf_cur += len;
            Ok(len)
        }
    }
}

impl<R: BufRead> GzDecoder<R> {
    /// Creates a new decoder from the given reader, immediately parsing the
    /// gzip header.
    pub fn new(mut r: R) -> GzDecoder<R> {
        let mut buf = Vec::with_capacity(10); // minimum header length
        let mut header = None;

        let result = {
            let mut reader = Buffer::new(&mut buf, &mut r);
            read_gz_header(&mut reader)
        };

        let state = match result {
            Ok(hdr) => {
                header = Some(hdr);
                GzState::Body
            },
            Err(ref err) if io::ErrorKind::WouldBlock == err.kind()
                => GzState::Header(buf),
            Err(err) => GzState::Err(err)
        };

        GzDecoder {
            inner: state,
            reader: CrcReader::new(deflate::bufread::DeflateDecoder::new(r)),
            multi: false,
            header
        }
    }

    fn multi(mut self, flag: bool) -> GzDecoder<R> {
        self.multi = flag;
        self
    }
}

impl<R> GzDecoder<R> {
    /// Returns the header associated with this stream, if it was valid
    pub fn header(&self) -> Option<&GzHeader> {
        self.header.as_ref()
    }

    /// Acquires a reference to the underlying reader.
    pub fn get_ref(&self) -> &R {
        self.reader.get_ref().get_ref()
    }

    /// Acquires a mutable reference to the underlying stream.
    ///
    /// Note that mutation of the stream may result in surprising results if
    /// this encoder is continued to be used.
    pub fn get_mut(&mut self) -> &mut R {
        self.reader.get_mut().get_mut()
    }

    /// Consumes this decoder, returning the underlying reader.
    pub fn into_inner(self) -> R {
        self.reader.into_inner().into_inner()
    }
}

impl<R: BufRead> Read for GzDecoder<R> {
    fn read(&mut self, into: &mut [u8]) -> io::Result<usize> {
        let GzDecoder { inner, header, reader, multi } = self;

        loop {
            *inner = match mem::replace(inner, GzState::End) {
                GzState::Header(mut buf) => {
                    let result = {
                        let mut reader = Buffer::new(&mut buf, reader.get_mut().get_mut());
                        read_gz_header(&mut reader)
                    };
                    let hdr = result
                        .map_err(|err| {
                            if io::ErrorKind::WouldBlock == err.kind() {
                                *inner = GzState::Header(buf);
                            }

                            err
                        })?;
                    *header = Some(hdr);
                    GzState::Body
                },
                GzState::Body => {
                    if into.is_empty() {
                        *inner = GzState::Body;
                        return Ok(0);
                    }

                    let n = reader.read(into)
                        .map_err(|err| {
                            if io::ErrorKind::WouldBlock == err.kind() {
                                *inner = GzState::Body;
                            }

                            err
                        })?;

                    match n {
                        0 => GzState::Finished(0, [0; 8]),
                        n => {
                            *inner = GzState::Body;
                            return Ok(n);
                        }
                    }
                },
                GzState::Finished(pos, mut buf) => if pos < buf.len() {
                    let n = reader.get_mut().get_mut()
                        .read(&mut buf[pos..])
                        .and_then(|n| if n == 0 {
                            Err(io::ErrorKind::UnexpectedEof.into())
                        } else {
                            Ok(n)
                        })
                        .map_err(|err| {
                            if io::ErrorKind::WouldBlock == err.kind() {
                                *inner = GzState::Finished(pos, buf);
                            }

                            err
                        })?;

                    GzState::Finished(pos + n, buf)
                } else {
                    let (crc, amt) = finish(&buf);

                    if crc != reader.crc().sum() || amt != reader.crc().amount() {
                        return Err(corrupt());
                    } else if *multi {
                        let is_eof = reader.get_mut().get_mut()
                            .fill_buf()
                            .map(|buf| buf.is_empty())
                            .map_err(|err| {
                                if io::ErrorKind::WouldBlock == err.kind() {
                                    *inner = GzState::Finished(pos, buf);
                                }

                                err
                            })?;

                        if is_eof {
                            GzState::End
                        } else {
                            reader.reset();
                            reader.get_mut().reset_data();
                            header.take();
                            GzState::Header(Vec::with_capacity(10))
                        }
                    } else {
                        GzState::End
                    }
                },
                GzState::Err(err) => return Err(err),
                GzState::End => return Ok(0)
            };
        }
    }
}

#[cfg(feature = "tokio")]
impl<R: AsyncRead + BufRead> AsyncRead for GzDecoder<R> {}

impl<R: BufRead + Write> Write for GzDecoder<R> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.get_mut().write(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        self.get_mut().flush()
    }
}

#[cfg(feature = "tokio")]
impl<R: AsyncWrite + BufRead> AsyncWrite for GzDecoder<R> {
    fn shutdown(&mut self) -> Poll<(), io::Error> {
        self.get_mut().shutdown()
    }
}

/// A gzip streaming decoder that decodes all members of a multistream
///
/// A gzip member consists of a header, compressed data and a trailer. The [gzip
/// specification](https://tools.ietf.org/html/rfc1952), however, allows multiple
/// gzip members to be joined in a single stream. `MultiGzDecoder` will
/// decode all consecutive members while `GzDecoder` will only decompress
/// the first gzip member. The multistream format is commonly used in
/// bioinformatics, for example when using the BGZF compressed data.
///
/// This structure exposes a [`BufRead`] interface that will consume all gzip members
/// from the underlying reader and emit uncompressed data.
///
/// [`BufRead`]: https://doc.rust-lang.org/std/io/trait.BufRead.html
///
/// # Examples
///
/// ```
/// use std::io::prelude::*;
/// use std::io;
/// # use flate2::Compression;
/// # use flate2::write::GzEncoder;
/// use flate2::bufread::MultiGzDecoder;
///
/// # fn main() {
/// #   let mut e = GzEncoder::new(Vec::new(), Compression::default());
/// #   e.write_all(b"Hello World").unwrap();
/// #   let bytes = e.finish().unwrap();
/// #   println!("{}", decode_reader(bytes).unwrap());
/// # }
/// #
/// // Uncompresses a Gz Encoded vector of bytes and returns a string or error
/// // Here &[u8] implements BufRead
///
/// fn decode_reader(bytes: Vec<u8>) -> io::Result<String> {
///    let mut gz = MultiGzDecoder::new(&bytes[..]);
///    let mut s = String::new();
///    gz.read_to_string(&mut s)?;
///    Ok(s)
/// }
/// ```
#[derive(Debug)]
pub struct MultiGzDecoder<R>(GzDecoder<R>);

impl<R: BufRead> MultiGzDecoder<R> {
    /// Creates a new decoder from the given reader, immediately parsing the
    /// (first) gzip header. If the gzip stream contains multiple members all will
    /// be decoded.
    pub fn new(r: R) -> MultiGzDecoder<R> {
        MultiGzDecoder(GzDecoder::new(r).multi(true))
    }
}

impl<R> MultiGzDecoder<R> {
    /// Returns the current header associated with this stream, if it's valid
    pub fn header(&self) -> Option<&GzHeader> {
        self.0.header()
    }

    /// Acquires a reference to the underlying reader.
    pub fn get_ref(&self) -> &R {
        self.0.get_ref()
    }

    /// Acquires a mutable reference to the underlying stream.
    ///
    /// Note that mutation of the stream may result in surprising results if
    /// this encoder is continued to be used.
    pub fn get_mut(&mut self) -> &mut R {
        self.0.get_mut()
    }

    /// Consumes this decoder, returning the underlying reader.
    pub fn into_inner(self) -> R {
        self.0.into_inner()
    }
}

impl<R: BufRead> Read for MultiGzDecoder<R> {
    fn read(&mut self, into: &mut [u8]) -> io::Result<usize> {
        self.0.read(into)
    }
}

#[cfg(feature = "tokio")]
impl<R: AsyncRead + BufRead> AsyncRead for MultiGzDecoder<R> {}

impl<R: BufRead + Write> Write for MultiGzDecoder<R> {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.get_mut().write(buf)
    }

    fn flush(&mut self) -> io::Result<()> {
        self.get_mut().flush()
    }
}

#[cfg(feature = "tokio")]
impl<R: AsyncWrite + BufRead> AsyncWrite for MultiGzDecoder<R> {
    fn shutdown(&mut self) -> Poll<(), io::Error> {
        self.get_mut().shutdown()
    }
}